Monday, May 2, 2011

1st May update PV and Meters

1 May '11: Aaah, the Wedding hangover.... and my daughter cycled 150 miles during the wedding and a couple of days after - pity she wasn't connected to a dynamo! Cycling to Cambridge during the wedding wasn't a tribute to the new Duke, as his title was announced after the ride started.
    Today we had a record Photovoltaic harvest for this time of year, 24.20 kWh, even though it is still 7 weeks before the Summer Solstice. This is explained by the ultra clear sky, but also by the very nippy North East wind that helped keep the panels cool all morning. There were two days with scores of over 24 kWh in a day during May 2010, so this is a good start. But really.... I wish for a day of heavy rain to water the garden and all the other gardens!
    However, all is not perfect, each of Feb, Mar and Apr 2011 have gathered lower PV figures than the same months of last year, and maybe I should get 'Brian' in to clean them with his long brush! (or do it myself.). With only about 10 mins of rain in the whole of April, surely it should have been a higher PV harvest?
  On the metering front, things are still going well. The house meter is about to dip below 5,400 kWh for a whole year, and the Heat Pump is about to go below 3,400 kWh. (This heat pump figure includes the Heating, Hot water and Underfloor circulating pump). The Surya Sunboxes have had a good week despite the dormancy of the heat pump, and they have scored 3,030 kWh for the last year.

TV Aerial shadow: One annoyance is bothering me which is that the summer afternoons have a distinct 300W dip in the Bell Curve while the shadow persists - this can be seen above from 3pm till 4.30pm when the Sun is finally around to the West. Any shading on the entire array will cause a loss.
  This doesn't need shifting sideways. I think the vertical tube is held in a clamp, and can be moved downwards.


  1. David,

    The pipe is SDR11, and 40mm refers to the OD. The wall thickness is 1/11 of the OD. So your calc of cross sectional area is over by around 150%!. You can work out the time taken for the glycol to go around the circuit by calculating the flow rate. If you knoww the conc of glycol u can dtermine the specific heat capacity - and then using the heat eqn you can calc backwards if you know the heat output acorss the heat pump and the flow and return temps across the heat pump. You will then have a flow rate and also the cross sectional area - you can then calc the residence time in the tube.

  2. Chris I have a section of the pipe to hand, and the outer diam is 40mm and the internal diameter is 32mm, making the cross sectional area for liquid to be 804 mm2. (Pi * R2) I have more than one tape measure to check this with, Donald Trump doesnt need to send private detectives for it.
    Is a 50-50 glycol water mixture about the same specific heat as water? The glycol is there as anti-freeze. Surely, if you could be sure it would never freeze this baby could run on neat water, surely?

  3. Chris, the SH of water is 4.2 and that of Glycol (neat) is 2.47. If you have a 50-50 or 40-60 mix, do you simply interpolate the two values?

  4. David,

    Note quite - I have many of the neccesary formulas for the properties of glycol- water solutions. Surely you do not have a 50-50 mix - that would be very viscous. Yes if you can be assured that the glycol-water temp never dips below zero then you can use pure water (but it would be best to add inhibitors etc).

    By the way the ID is 32.727mm

    did you measure the concentration with a refractometer?


  5. Well Ice Energy told me the original mix would have been 50-50, so I was safe to make the top up of 60 litres with 20-40 ratio.
    If I did my very roundabout calculation with 32mm diameter, how can I be 150% oversize if the real diam is 32.727?


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